Synthesis of lithium lanthanum zirconate from nanocrystalline lanthanum zirconate

ABSTRACT

Fabricating a layer including lithium lanthanum zirconate (Li7La3Zr2O12) layer includes forming a slurry including lanthanum zirconate (La2Zr2O7) nanocrystals, a lithium precursor, and a lanthanum precursor in stoichiometric amounts to yield a dispersion including lithium, lanthanum, and zirconium. In some cases, the dispersion includes lithium, lanthanum, and zirconium in a molar ratio of 7:3:2. In certain cases, the slurry includes excess lithium. The slurry is dispensed onto a substrate and dried. The dried slurry is calcined to yield the layer including lithium lanthanum zirconate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Application No. 62/667,383filed on May 4, 2018, which is incorporated by reference herein in itsentirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under the awardDMR-1553519 from the National Science Foundation. The government hascertain rights in this invention.

TECHNICAL FIELD

This invention relates the synthesis of lithium lanthanum zirconate(LLZO) from lanthanum zirconate (LZO) nanocrystals. The LLZO can be inthe form of a layer (e.g., a thin film) or other structure.

SUMMARY

Lithium lanthanum zirconate (Li₇La₃Zr₂O₁₂, LLZO) is a fast ion conductorfor Li-ions suitable for use as a solid electrolyte that can enhance theenergy density and safety of Li-ion batteries. Advantages related toreduction in the size of this material to nanometric dimensions includethe ability to stabilize the highly conducting cubic phase without theneed for extrinsic dopants, enhanced densification and sinteringproperties, and lower temperature and lower cost preparation methods.Further, beginning with ultrafine crystals may enable fine-tuning of thefinal grain size of a dense LLZO film, which may in turn enableHall-Petch strengthening of the final dense ceramic. As describedherein, LLZO thin films are fabricated from salts of lithium andlanthanum (and optionally a dopant such as aluminum, gallium, calcium,tantalum, niobium, or molybdenum, or a combination thereof) mixed withlanthanum zirconate nanocrystals. Stoichiometric Li- and La-precursorsare mixed with these nanocrystals to yield a slurry suitable for tapecasting resulting in thin films, which after calcination and sintering,results in LLZO thin films having fine grain structure and superiormechanical properties (e.g., flexible, non-brittle) suitable for facileincorporation into battery fabrication schemes. In some implementations,lanthanum zirconate nanocrystals containing excess lanthanum andoptionally a dopant such as aluminum, gallium, calcium, tantalum,niobium, molybdenum, or a combination thereof is mixed with salts oflithium and then calcined and sintered to form LLZO.

In a first general aspect, fabricating a layer including lithiumlanthanum zirconate (Li₇La₃Zr₂O₁₂) includes forming a slurry includinglanthanum zirconate (La₂Zr₂O₇) nanocrystals, a lithium-containingcompound, and a lanthanum-containing compound to yield a dispersionincluding lithium, lanthanum, and zirconium. The slurry is dispensedonto a substrate and dried, and the dried slurry is calcined to yieldthe layer including lithium lanthanum zirconate.

Implementations of the first general aspect may include one or more ofthe following features.

The lithium-containing compound can include lithium nitrate. Thelanthanum-containing compound can include lanthanum nitrate.

In some cases, the slurry includes a dopant, such as one or more ofaluminum, gallium, tantalum, niobium, and molybdenum. In some cases, theslurry includes a dispersant, such as one or more of a surfactant, fishoil, poly(acrylic acid) and salts thereof, poly(methacrylic acid) andsalts thereof, and phosphate esters. In some cases, the slurry includesa plasticizer, such as one or more of polyethylene glycol, benzyl butylphthalate, and glycerol. In some cases, the slurry includes a binder,such as polyvinylbutyral.

Disposing the slurry on the substrate can include casting the slurry onthe substrate (e.g., tape-casting or spin-casting) or dip-coating thesubstrate in the slurry. Calcining the dried slurry can include heatingthe dried slurry at a temperature between 700° C. and 1200° C. for a fewminutes to several hours. In some cases, forming the slurry includesforming the slurry in one or more of methanol and ethanol.

The lanthanum zirconate nanocrystals typically have an average diameterin a range of 5 nm to 50 nm, or in a range of 10 nm to 30 nm. The layerincluding lithium lanthanum zirconate typically has a grain size of lessthan 300 nm. A thickness of the layer is typically in a range of 1 μm to500 μm, or 5 μm to 500 μm.

The lithium lanthanum zirconate can be cubic phase lithium lanthanumzirconate. The dispersion can include lithium, lanthanum, and zirconiumin a molar ratio of 7:3:2, or in a molar ratio of more than 7 moleslithium to 3 moles lanthanum to 2 moles zirconium (e.g., an excess oflithium).

In a second general aspect, synthesizing lithium lanthanum zirconate(Li₇La₃Zr₂O₁₂) includes combining lanthanum zirconate (La₂Zr₂O₇)nanocrystals having excess lanthanum with one or more salts of lithiumto yield a mixture; calcining the mixture to yield a calcined mixture;and sintering the calcined mixture to yield lithium lanthanum zirconate.

Implementations of the second general aspect may include one or more ofthe following features.

The lanthanum zirconate nanocrystals can include a dopant. The one ormore salts of lithium can be molten. The mixture can be in the form of aslurry.

The details of one or more embodiments of the subject matter of thisdisclosure are set forth in the accompanying drawings and thedescription. Other features, aspects, and advantages of the subjectmatter will become apparent from the description, the drawings, and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustrating the formation of Li₇La₃Zr₂O₁₂(LLZO) thin films from La₂Zr₂O₇ (LZO) nanoparticle slurries.

FIG. 2 shows a representative X-ray diffraction (XRD) pattern of LZOformed from molten salt synthesis (used as a precursor to LLZO).

FIGS. 3A-3D show representative transmission electron microscopy (TEM)images of the LZO used as a precursor.

FIG. 4 shows a representative XRD pattern of LLZO formed aftercalcination of a tape-cast film at 900° C. for 6 hours.

FIGS. 5A and 5B show representative TEM images of off-stoichiometricnanocrystals with a nominal composition of La_(2.4)Zr_(1.12)Ta_(0.48)O₇(corresponding to a La:Zr:Ta ratio of 3:1.4:0.6) used as a precursor tomake LLZO. FIG. 5C shows XRD patterns of various off-stoichiometric,doped, and co-doped LZO nanocrystals synthesized using molten saltreaction compared to stoichiometric nanocrystals and powder synthesizedusing solid state reaction (SSR).

FIGS. 6A and 6B show representative XRD patterns of products obtainedafter using nanocrystals with a nominal composition ofLa_(2.4)Zr_(1.12)Ta_(0.48)O_(7+x) (LZTO), where x=0.04, as precursors toprepare Ta-doped LLZO (LLZTO) with a nominal composition ofLi_(6.4)La₃Ta_(0.6)Zr_(1.4)O₁₂ in a molten salt (NaOH:KOH eutectic)containing different amounts of Li₂O₂ at different reaction temperaturesand reaction times. FIGS. 6C and 6D are representative scanning electronmicroscopy (SEM) and high-angle annular dark-field (HAADF) STEM images,respectively, of LLZTO synthesized by molten salt synthesis (MSS) usingoff-stoichiometric doped LZO as the La, Zr, and Ta source.

FIGS. 7A and 7B show schematics illustrating the formation of LLZTOparticles from the reaction of LZTO nanocrystals in a molten saltreaction (NaOH:KOH eutectic) containing Li₂O₂. The LLZTO particles canthen be processed into a slurry and fabricated into a thin film usingtape-casting.

FIG. 8 shows a schematic illustrating the formation of a LLZTO pelletfrom LZTO nanocrystals by solid state reaction with a lithium source(e.g., LiOH) after high temperature sintering.

FIG. 9A shows a representative XRD pattern of LLZTO formed fromsintering LZTO (nominal composition La_(2.4)Zr_(1.12)Ta_(0.48)O₇)nanocrystals with stoichiometric anhydrous LiOH (i.e., 6.4 moles LiOH to3 moles La) with 5% excess and sintering at 1200° C. FIG. 9B shows arepresentative SEM image of the pellet fracture surface. FIG. 9C showsan enlarged view of an identified region in FIG. 9B.

DETAILED DESCRIPTION

Lithium lanthanum zirconate (Li₇La₃Zr₂O₁₂, LLZO) can be synthesizedusing a variety of methods, such as solid-state reaction, sol-gel,chemical or atomic layer deposition, and molten salt synthesis. In mostof these synthesis methods, La₂Zr₂O₇ (LZO) is formed as an intermediatephase at lower temperatures, shorter reaction times, or both thanrequired to obtain LLZO. Further reaction of the LZO with Li- andLa-precursors lead to the formation of LLZO. Hence, one route towardsobtaining nanostructured LLZO is to begin with nanostructured LZO as astarting phase.

Molten salt synthesis (MSS) (sometimes known as “salt melt synthesis” orthe “molten salt method”) can be used to obtain various-sized particlesof ceramics from generally inexpensive precursors at temperatures ortimes lower than those required in solid state reactions. In MSS,precursors including or consisting of metal oxides or metal salts aremixed intimately with a salt (or salt mixture, often a eutectic),followed by heat treatment above the melting point of the salt(s) toprovide the thermodynamic driving force for dissolution of theprecursors and to promote the formation of the desired crystallinephase. Synthesis of LZO in a eutectic mixture of sodium hydroxide andpotassium hydroxide (41:59 wt % NaOH:KOH) is also described. In thisprocess, MSS is used to obtain non-agglomerated LZO nanopowders in largequantities suitable as a reagent for formation of LLZO. These moreuniform and fine powders may enable roll-to-roll processing ofelectrolyte materials, e.g., tape-casting, and thus better incorporationinto practical battery production methods. This factor can help overcomethe challenge of using a brittle, crystalline ceramic as an electrolyte.On a lab scale, tens of grams of uniform LZO can be obtained in a matterof hours using a single small furnace, indicating that this synthesisapproach provides a scalable method of LLZO production.

FIG. 1 depicts the formation of LLZO thin films from LZO nanoparticleslurries. LZO nanocrystals 100 with diameters of about 20 nm may beprepared by MSS in a eutectic mixture of NaOH and KOH at elevatedtemperatures (e.g., 400-550° C.) for 1-4 hours, among other possiblemethods. LZO nanocrystals 100 can also be synthesized using othermethods such as hydrothermal synthesis, sol-gel synthesis, andsalt-assisted combustion synthesis. These LZO nanocrystals are dispersedin polar media (e.g., water and low molecular weight alcohols such asmethanol or ethanol) or non-aqueous organic solvent systems (such asethanol and methyl ethyl ketone, or ethanol and toluene), sometimes withthe aid of a dispersant, to yield slurry 102 of LZO nanocrystals. Insome implementations, slurry 102 includes LiNO₃, La(NO₃)₃, M(NO₃)_(n),or a combination thereof, where M includes one or more of Al, Ga, Ta,Nb, and Mo, and n=+3 or +5. In some implementations, slurry 102 includesone or more of a dispersant, a plasticizer, and a binder in the solvent.

The LZO nanocrystals can then act as substrates upon which to form LLZOif suitable Li-, La-, and other (e.g., dopant) precursors are added inappropriate (e.g., stoichiometric) quantities to the slurry. Slurry 102can be cast into LZO layer 104 and dried, followed by calcination tocomplete the conversion of LZO to LLZO layer 106. In some cases, layers104 and 106 are thin films. Layers 106 of LLZO can be formed by methodsincluding tape-casting, spin-casting, and dip-coating to convert thenanocrystalline LZO into fine-grained LLZO films by solid phase reactionand subsequent sintering.

In some implementations, LZO nanocrystals that contain excess amount oflanthanum and optionally dopants are prepared such that only suitableamounts of Li precursor is required in order to transform the LZO intoLLZO. By including all of the required elements, except for Li, withinthe nanocrystal, the transformation to LLZO can be achieved in a facilemanner in a molten salt reaction or calcination as discussed previously.

EXAMPLES Example 1: Synthesis of La₂Zr₂O₇(LZO) Nanocrystals andTransformation to Al-Doped LLZO by Tape-Casting

All reagents used were of ACS grade or higher and used as-received.Sodium Hydroxide (NaOH), potassium hydroxide (KOH), lithium nitrate(LiNO₃), zirconium oxynitrate (ZrO(NO₃)₂) hydrate, and aluminum nitrate(Al(NO₃)₃) nonahydrate (used to provide Al³⁺ dopants to stabilize thecubic structure of LLZO) were obtained from Sigma-Aldrich. Lanthanumnitrate (La(NO₃)₃) hexahydrate was obtained from Alfa Aesar. HPLC grademethanol was obtained from BDH, poly(vinylbutyral) was obtained fromAlfa-Aesar, and PEG 400 was obtained from Aldrich. Other reagentssimilar to those described above may also be used.

To prepare the hydroxide mixture, 41 wt % NaOH and 59 wt % KOH weremixed followed by melting above 400-550° C. (melting point of NaOH—KOHeutectic mixture ˜170° C.). The LZO nitrate precursors were prepared bymixing La(NO₃)₃, and ZrO(NO₃)₂ in a 1:1 molar ratio and grindingthoroughly with a mortar and pestle.

The premixed nitrate precursor salts were then added carefully to thepre-heated molten hydroxide mixture, which produced an evolution ofwater vapor and other gases (e.g., NOR). Once the precursors were addedto the molten hydroxides, the crucible was briefly mixed by agitationand reintroduced to the furnace for a few minutes to a few hours.

After the synthesis, ultrapure water (>18 MOhm cm) was added to thecooled crucibles, and the suspension was ultrasonicated using animmersion probe (Cole-Parmer 500 W Ultrasonic Processor) to rapidlydissolve the fused hydroxides and generate a slurry of powder.Subsequently, the slurry was vacuum filtered using poly(vinylidenefluoride) membranes (0.22 μm pore size, DuraPore, EMD corporation) andwashed with at least 150 mL of water followed by 50 mL of methanol (BDH,HPLC grade) to facilitate fast drying. Conversely, the solution may bewashed by repeated centrifugation, decantation of supernatant solution,addition of further ultrapure water and resuspension of powders byultrasonication. Finally, the filter membranes or centrifuge tubes alongwith the wet powder cakes were placed in an oven at elevated temperature(e.g., 50° C.) and dried in air. After drying, the powders were removedfrom the filter membranes or tubes and lightly ground with a mortar andpestle. FIG. 2 shows a representative X-ray diffraction (XRD) pattern ofthe as-synthesized LZO nanocrystals, and FIGS. 3A-3D show representativetransmission electron microscopy (TEM) images of the LZO nanocrystals300, 302, 304, and 306, respectively.

Formation of a slurry suitable for tape-casting can be performed bymixing nanocrystalline LZO and methanol in a 1:2 ratio (by mass).Subsequently, stoichiometric nitrates of Li, La, and optionally Al (asdopant) may be dissolved in the methanolic slurry following by mixingwith e.g. ultrasound or planetary ball milling. A dispersant (e.g.,surfactant, fish oil, poly(acrylic acid) and salts thereof,poly(methacrylic acid) and salts thereof, and phosphate esters) may beadded at this stage as needed. Subsequently, a binder such aspoly(vinylbutyral) may be added comprising a few weight percent of thetotal slurry. The binder can enable formation of a cohesive film upondrying and removal of the solvent. Optionally, a plasticizer such aspoly(ethylene glycol) may be added to increase the flexibility to theresultant film. Once these components are added to the slurry, theslurry is ball-milled using, for example, a planetary ball mill forextended periods of time to result in a stable slurry with a lowsettling rate. This slurry may be cast using various methods to formthin films which, upon calcination and sintering, result in thin (30-500μm) LLZO films.

The aforementioned slurry may be tape cast (e.g., using a wire-wound rodcoater) in order to form a thin slurry film. Upon drying under thedesired conditions (e.g., ambient conditions, elevated temperature,controlled humidity, etc.), a thin, uniform film includingnanocrystalline LZO covered in a thin polymer film results. Added Li-,La-, and other precursors are dispersed within this film, adhered to thesurface of the LZO crystals, or both. This composite thin film may thenbe calcined and sintered to yield a film of LLZO. Calcining may includeheating at 900° C. for several hours. A representative XRD pattern of acalcined tape showing mostly LLZO (0.3≥x≥0 or 0.25≥x≥0.2) with a smallamount of LZO is shown in FIG. 4.

Example 2: Synthesis of Off-Stoichiometric, Doped LZO Nanocrystals andTransformation to Ta-Doped LLZO

All reagents used were of ACS grade or higher and used as-received.Sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium nitrate(LiNO₃), zirconium oxynitrate (ZrO(NO₃)₂) hydrate, tantalum (V)pentoxide (used to provide Ta⁵⁺ dopants to stabilize the cubic structureof LLZO), sodium fluoride and calcium nitrate tetrahydrate (used toprovide Ca²⁺ co-dopants) were obtained from Sigma-Aldrich. Lanthanumnitrate (La(NO₃)₃) hexahydrate was obtained from Alfa-Aesar. Lithiumperoxide (Li₂O₂) was obtained from Acros Organics.

The NaOH:KOH eutectic mixture and nitrate salts were prepared in asimilar manner as described in Example 1. Typical reaction temperatureswere between 400-550° C. with reaction times of 1-4 h. After thesynthesis, the products were washed with ultrapure deionized water asdescribed in Example 1.

Representative low and high magnification TEM images of the synthesizedoff-stoichiometric LZO nanocrystals 500, 502 (nominal compositionLa_(2.4)Zr_(1.12)Ta_(0.48)O₇) are shown in FIGS. 5A and 5B,respectively, showing the nanometric particle sizes. XRD patterns of theLZO nanocrystals with various nominal compositions are shown in FIG. 5C,along with XRD patterns for La₂Zr₂O₇ bulk powder synthesized using solidstate reaction (SSR) and stoichiometric La₂Zr₂O₇ nanocrystalssynthesized as described in Example 1 for comparison. The peakbroadening in the XRD patterns of the nanocrystal samples compared tothe SSR sample arises due to the nanometric particle sizes. The XRDresults show that it is feasible to synthesize LZO nanocrystals withexcess lanthanum, tantalum doping, calcium and tantalum co-doping, andcalcium, tantalum and fluorine co-doping while maintaining the samepyrochlore structure using molten salt synthesis. Only small amounts ofLa(OH)₃ and other unidentified impurity phases were observed in the XRDpattern, suggesting that the dopants were successfully incorporated intothe LZO nanocrystals.

As an example, nanocrystals with nominal compositionLa_(2.4)Zr_(1.12)Ta_(0.48)O_(7+x) (LZTO) where x=0.04 were used asprecursors to prepare Ta-doped LLZO (LLZTO) with nominal compositionLi_(6.4)La₃Ta_(0.6)Zr_(1.4)O₁₂. The nanocrystals were added to a moltensalt flux consisting of 5 g of LiNO₃ and LiOH (1:1 mass ratio) withbetween 0.75-1.5 g of Li₂O₂ as additive to provide reactive oxygenspecies. Optionally, the LZTO nanocrystals can be ground together withan equal mass of anhydrous LiNO₃ to dilute them, de-agglomerate them,and help with mixing upon addition to the molten salt flux. Reactiontemperature between 400-550° C. were studied, with the reaction timevaried from 1-5 h. The products were washed with de-ionized water asdescribed previously. XRD patterns of the formed products are shown inFIGS. 6A and 6B. The results show that the amount of Li₂O₂ added to thesalt melt, the reaction temperature, and the reaction time play a roleon the transformation of LZTO to LLZTO. As shown in FIG. 6A, when noLi₂O₂ was added, the product remained mostly LZTO after reaction at 400and 500° C., Adding 1.5 g of Li₂O₂ was sufficient to form LLZTO after 5h at 400° C., and only 1 h at 500 and 550° C. Other than some residualLiOH from the molten salt, no other crystalline impurity phases wereobserved. As shown in FIG. 6B, decreasing the amount of Li₂O₂ additiveto 0.75 g required a longer reaction time of 3 h to transform the LZTOto LLZTO at 500 and 550° C. The Li₂O₂ likely plays an important role inproviding reactive species for the reaction to proceed. RepresentativeSEM and TEM images of LLZTO particles 600 and 602 formed using LZTO at550° C. are shown in FIGS. 6C and 6D, respectively, showing that theyhave submicron diameters. These particles can be used to prepare thinfilms of LLZTO using tape-casting and other techniques describedearlier. These results show that LZTO nanocrystal precursors can besuccessfully transformed to LLZTO after reaction with Li in a highlybasic molten salt flux.

FIGS. 7A and 7B depict the formation of LLZTO powders from LZTOnanoparticles in the molten salt, followed by casting of the LLZTOpowders into thin films. As depicted in FIG. 7A, LZTO nanoparticles 700are added to a molten salt flux 702 including 5 g of LiNO₃ and LiOH (1:1mass ratio) with between 0.75-1.5 g of Li₂O₂ as an additive to providereactive oxygen species. Optionally, the LZTO nanocrystals can be groundtogether with an equal mass of anhydrous LiNO₃ to dilute them,de-agglomerate them, and help with mixing upon addition to the moltensalt flux. Reaction temperatures between 400-550° C. and reaction timesbetween 1-5 h can be used. The reaction mixture is washed to yield LLZTOparticles 704. As depicted in FIG. 7B, LLZTO nanoparticles 710 arecombined with a solvent and one or more of a dispersant, a plasticizer,and a binder to form slurry 712. Slurry 712 is cast to form a layer 714,and layer 714 is calcined to yield LLZO layer 716.

As another example, LZTO (nominal compositionLa_(2.4)Zr_(1.12)Ta_(0.48)O₇) nanocrystals were transformed to LLZTO bysintering with a lithium source (e.g. LiOH, Li₂CO₃, Li₂O) in the form ofpellet. As depicted in FIG. 8, LZTO nanoparticles 800 are mixed withLiOH (e.g., stoichiometric anhydrous LiOH (i.e. 6.4 moles LiOH to 3moles La) with 5% excess (by mass)) by slurry grinding in a mortar andpestle with water or methanol as the solvent followed by drying, andthen pressed into pellets 804 (e.g., 7 mm pellets) and sintered to yieldLLZTO pellets 806. Sintering may be achieved using a ramp rate of 4°C./min to the target temperature. After sintering at 1200° C. for 6 h,pellets with relative density of 79% were obtained. Sintering at 900° C.for 2 h, followed by 1200° C. for 4 h resulted in pellets with slightlyhigher relative density of 82%. Electrochemical impedance spectroscopywas performed at room temperature after applying graphite contacts toeither side of the pellet. The Li ionic conductivity was 0.07 mS/cm forthe pellet sintered at 1200° C. for 6 h, while the conductivityincreased to 0.23 mS/cm for the pellet sintered with the lowertemperature step. FIG. 9A shows an XRD pattern of pellet 804 sintered at900° C. (2 h) then 1200° C. (4 h). FIG. 9B shows an SEM image offracture surfaces of pellet 804, and FIG. 9C shows a magnified view ofregion 900 in FIG. 9B. The XRD pattern showed that the LZTO nanocrystalswere successfully transformed to LLZTO without forming any secondaryphases. The SEM images show that the pellet has a highly densemicrostructure and displayed transgranular fracture; however, some largepores were still present which indicate that the sintering conditionsneed to be further optimized.

These results show that LZTO nanocrystals can serve as precursors toform LLZTO with good ionic conductivity after reaction with lithium. Thetransformation was successfully conducted in a lithium-containing moltensalt flux at moderate temperatures (400-550° C.) as well as in asolid-state reaction with a lithium source using high temperaturesintering (1200° C.). It is expected that this transformation will alsobe feasible in thin films such as those prepared by tape-casting from aslurry containing LZTO nanocrystals and a lithium source.

Although this disclosure contains many specific embodiment details,these should not be construed as limitations on the scope of the subjectmatter or on the scope of what may be claimed, but rather asdescriptions of features that may be specific to particular embodiments.Certain features that are described in this disclosure in the context ofseparate embodiments can also be implemented, in combination, in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment can also be implemented in multipleembodiments, separately, or in any suitable sub-combination. Moreover,although previously described features may be described as acting incertain combinations and even initially claimed as such, one or morefeatures from a claimed combination can, in some cases, be excised fromthe combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

Particular embodiments of the subject matter have been described. Otherembodiments, alterations, and permutations of the described embodimentsare within the scope of the following claims as will be apparent tothose skilled in the art. While operations are depicted in the drawingsor claims in a particular order, this should not be understood asrequiring that such operations be performed in the particular ordershown or in sequential order, or that all illustrated operations beperformed (some operations may be considered optional), to achievedesirable results.

Accordingly, the previously described example embodiments do not defineor constrain this disclosure. Other changes, substitutions, andalterations are also possible without departing from the spirit andscope of this disclosure.

What is claimed is:
 1. A method of fabricating a layer comprisinglithium lanthanum zirconate (Li₇La₃Zr₂O₁₂), the method comprising:forming a slurry comprising lanthanum zirconate (La₂Zr₂O₇) nanocrystals,a lithium-containing compound, and a lanthanum-containing compound toyield a dispersion comprising lithium, lanthanum, and zirconium;dispensing the slurry onto a substrate; drying the slurry to form adried slurry; and calcining the dried slurry to yield the layercomprising lithium lanthanum zirconate.
 2. The method of claim 1,wherein the lithium-containing compound comprises lithium nitrate. 3.The method of claim 1, wherein the lanthanum-containing compoundcomprises lanthanum nitrate.
 4. The method of claim 1, wherein theslurry further comprises a dopant.
 5. The method of claim 4, wherein thedopant comprises at least one of aluminum, gallium, tantalum, niobium,and molybdenum.
 6. The method of claim 1, wherein the slurry furthercomprises a dispersant.
 7. The method of claim 6, wherein the dispersantcomprises at least one of a surfactant, fish oil, poly(acrylic acid) andsalts thereof, poly(methacrylic acid) and salts thereof, and phosphateesters.
 8. The method of claim 1, wherein the slurry further comprises aplasticizer.
 9. The method of claim 8, wherein the plasticizer comprisespolyethylene glycol, benzyl butyl phthalate, glycerol, or a combinationthereof.
 10. The method of claim 1, wherein the slurry further comprisesa binder.
 11. The method of claim 10, wherein the binder comprisespolyvinylbutyral.
 12. The method of claim 1, wherein disposing theslurry on the substrate comprises casting the slurry on the substrate.13. The method of claim 12, wherein casting the slurry on the substratecomprises tape-casting or spin-casting.
 14. The method of claim 1,wherein disposing the slurry on the substrate comprises dip-coating thesubstrate in the slurry.
 15. The method of claim 1, wherein calciningthe dried slurry comprises heating the dried slurry at a temperaturebetween 700° C. and 1200° C. for a few minutes to several hours.
 16. Themethod of claim 1, wherein forming the slurry comprises forming theslurry in methanol, ethanol, or a combination thereof.
 17. The method ofclaim 1, wherein the lanthanum zirconate nanocrystals have an averagediameter in a range of 5 nm to 50 nm.
 18. The method of claim 1, whereinthe lanthanum zirconate nanocrystals have an average diameter in a rangeof 10 nm to 30 nm.
 19. The method of claim 1, wherein the layercomprises lithium lanthanum zirconate having a grain size of less than300 nm.
 20. The method of claim 1, wherein a thickness of the layer isin a range of 1 μm to 500 μm.
 21. The method of claim 1, wherein thelithium lanthanum zirconate is cubic phase lithium lanthanum zirconate.22. The method of claim 1, wherein the dispersion comprises lithium,lanthanum, and zirconium in a molar ratio of 7:3:2.
 23. The method ofclaim 1, wherein the dispersion comprises lanthanum and zirconium in amolar ratio of >7 moles lithium to 3 moles lanthanum to 2 moleszirconium.
 24. A method of synthesizing lithium lanthanum zirconate(Li₇La₃Zr₂O₁₂), the method comprising: combining lanthanum zirconate(La₂Zr₂O₇) nanocrystals comprising excess lanthanum with one or moresalts of lithium to yield a mixture; calcining the mixture to yield acalcined mixture; and sintering the calcined mixture to yield lithiumlanthanum zirconate.
 25. The method of claim 24, wherein the lanthanumzirconate nanocrystals further comprise a dopant.
 26. The method ofclaim 24, wherein the one or more salts of lithium are molten.
 27. Themethod of claim 24, wherein the mixture is a slurry.